Many intraocular diseases, such as proliferative retinopathies, occur due to neovascularization and/or leakage, which are caused in part by elevated vascular endothelial growth factor (“VEGF”) levels. These diseases include, but are not limited to, diabetic macular edema, diabetic proliferative retinopathy, retinopathy of prematurity, diabetic vitreal traction, wet macular degeneration and attendant neovascularization through Bruch's membrane between the choroid and retina, branch vein occlusion, complete retinal vein occlusion, maculopathies such as Best's disease, ischemic intraocular insult resulting in neovascular rubeotic (iris, anterior chamber angle neovascularization) glaucoma, and on or within the cornea coinciding with herpes simplex keratitis or a graft rejection.
Diabetic macular edema is the most common cause of vision loss among diabetics. Due to the increase in diabetes (both type I and type II) in developed countries such as the United States, diabetic macular edema is also the most common cause of vision loss among working-aged adults. Diabetic macular edema results when insulin resistance causes the vascular lining of blood vessels to thicken, resulting in capillary drop out, microaneurysms, ischemia, and leakage in the retina. The resulting hypoxia triggers an increase in the production of VEGFs, which in turn is a potent inducer of vascular permeability (leakage) and eventually results in the production of new blood vessels. These leaking blood vessels leak fluid into the macula causing the macula to swell resulting in vision loss, as well as eventually causing new blood vessel growth along the retina and into the vitreous causing proliferative retinopathy with high morbidity from bleeding and retinal detachment from resulting vitreous traction and scarring.
Macular degeneration is a disease of the eye that results in minor to severe impairment of the subject's sharp central vision, which is necessary for activities such as reading and driving. Age-related macular degeneration (“AMD”) afflicts an estimated 30 to 50 million people worldwide and is the leading cause of severe vision loss in Western societies. AMD disrupts the photoreceptors of the macula in one of two ways: (1) deposits of extracellular debris between Bruch's membrane and the retinal pigment epithelium known as “dry” macular degeneration and (2) breaks in Bruch's membrane that allow angiogenic blood vessels from the choroid to penetrate the retinal pigment epithelium known as “wet” macular degeneration. Dry AMD progresses slowly and is responsible for about 90% of AMD worldwide. Wet AMD can be sudden, severe and irreversible due to bleeding and scarring of the macular region including the fovea. Although wet AMD accounts for only 10% of AMD worldwide it is responsible for 90% of AMD-associated blindness.
VEGFR pathways are the main pharmaceutical targets of angiogenic suppression. Anti-angiogenesis drugs that target VEGFR pathways and are used in the eye include bevacizumab (Avastin®; Avastin is a registered trademark of Genentech, Inc.), ranibizumab (Lucentis®; Lucentis is a registered trademark of Genentech, Inc.) and recombinant fusion proteins such as aflibercept (Eylea®; Eylea is a registered trademark of Regeneron Pharmaceuticals, Inc.). These anti-VEGF protein drugs, which are too large to formulate for topical applications, require an injection monthly or several times per year to limit further vision loss. Currently, the morbidity, inconvenience, and expense of these injectables limit treatment to only severe pathologic states, because they are too invasive for routine prophylaxis prior to onset of significant pathology. For example, prophylactic administration would benefit wet macular degeneration such as in the presence of confluent or otherwise near confluent macular drusen of dry macular degeneration (a known predisposing risk factor for retinal pigment epithelium layer cracks and choroidal neovascularization). In another example, prophylactic administration would benefit the presence in diabetics of background diabetic retinopathy at various points of disease progression prior to the development of diabetic macular edema (e.g., macular or paramacular exudate, high density of dot blot hemorrhages) and most particularly prior to the development of proliferative retinopathy with or without macular edema such as in the presence of severe capillary drop out, and still more particularly in the presence of proliferative retinopathy prior to the development of fibrovascular retinopathy and attendant retinal traction and epiretinal formation. The inability to use these drugs as a prophylactic treatment modality limits their effectiveness in preventing early vision loss, but rather restricts them largely to treating only existing visual loss that can be extensive even at initial diagnosis.
Once in the vitreous humor these anti-VEGF proteins have a half-life of about 9 days, a high IC50 VEGFR inhibition value, fast release rate due to their hydrophilic nature and immediate dispersion within the vitreous towards tissue receptors, and interact with only one angiogenic receptor, VEGF. All of these qualities result in the need for a variety of formulation techniques required to attempt to enhance the residence time of the drug within the vitreous humor to achieve the more prolonged effect that would add safety and efficacy from a single injection. These formulation techniques include attempts at high concentrations, high volumes of bolus injection, emulsions, encapsulation techniques, and other sustained-release compositions; though their highly hydrophilic nature, relatively high concentrations required for efficacy (IC50 about 19 nM for Lucentis®), and limitations imposed on protein stability within solution restrict their potential for additional sustained duration via direct injection. As a result, although these drugs reduce disease morbidity they still add serious injection related morbidity exacerbated by the high frequency of injections required per year, where such injection induced morbidity includes but is not limited to endophthalmitis (intraocular severe infection often with complete vision loss), cataract, glaucoma, and vitreous traction that for many patients can be devastating.
To achieve 30-day duration of effect requires the maximum injectable volume tolerable by the human eye, about 50 uL, at about 0.50%. Such high bolus volumes frequently result in high intraocular pressure up to 49 mm Hg. Additionally, attempts to overcome these formulation and administration challenges can be problematic limited by properties intrinsic to these protein anti-VEGF molecules. For example, the pathology of the disease to be treated exposes these active agents to a variety of noxious stimuli including a more ischemic and acidic environment, which can cause these proteins to denature and degrade more rapidly and therefore compromise their potency when delivered via a sustained-release device. Particularly, the least invasive class of injectable sustained release implants, such as biodegradable implants such as Ozurdex®/Pozurdex® (Ozurdex is a registered trademark of Allergan, Inc.) releases glycolic and lactic acid that limit the usefulness of proteins for such devices due to rapid low pH denaturation. Finally, the efficacy of this class of drugs is limited by substantial tachyphylaxis and resistance that develops over time due to their inhibition of only VEGF's and not additional angiogenic receptors.
Additional tyrosine kinase receptors (“ancillary receptors”) involved in angiogenesis in addition to VEGFR have also been discovered and found to confer additional antiangiogenic benefit above that of VEGFR only inhibition as seen with protein anti-VEGF drugs such as Lucentis®, Avastin®, and Eylea®. The suppression of these ancillary receptors is known to enhance the anti-angiogenic effect of VEGFR pathway suppression. These ancillary receptors include platelet-derived growth factor receptors (“PDGFR”) a and (3, fibroblast-derived growth factor receptors (“FDGFR”) 1-4, c-KIT, and TIE 1-3, and particularly c-MET. Upregulation of c-MET is known to occur following anti-VEGF treatment and result in tachyphylaxis/resistance to such drugs with expression of angiogenic behavior resulting. Suppression of one or more of these ancillary receptors in conjunction with suppression of a VEGFR, including but not limited to c-MET, is common in the art and is known as multi-receptor tyrosine kinase inhibition. Multi-receptor tyrosine kinase inhibition for treatment of angiogenesis is known to decrease the incidence and severity of tachyphylaxis or resistance in response to suppression of a VEGFR alone. One such multi-tyrosine kinase inhibitor (“MTKI”) is cabozantinib (Cometriq®; Cometriq is a registered trademark of Exelixis, Inc.). Cabozantinib inhibits VEGFR2 at nearly 1/500th (0.214%) of Avastin® (bevacizumab, Genentech®/Roche®), with an IC50 of about 35 picomolar (“pM”) vs 1400 pM respectively in in vitro angiogenic assays for inhibition of human umbilical vascular endothelial cells (“HUVEC”). Cabozantinib also inhibits to various degrees other angiogenic receptors including PDGFR, FLT, TIE-2, and c-MET and was approved by the U.S. FDA for the treatment of medullary thyroid cancer.
Pharmaceutical use of tyrosine kinase inhibitors (“TKIs”) and more specifically MTKI's for intraocular use is complicated by their high permeability through cell membranes, their impermeability in solution and their high degrees of lipophilicity. These complications limit MTKI's ability to be formulated beyond their most common use for oral cancer treatment. Further, MTKI's such as cabozantinib when administered orally may lead to perforation of the colon. Intravenous administration is also problematic due to the short half-life of MTKI's such as cabozantinib.
Intravitreal injection is complicated by the sensitivity of the intraocular structures, particularly the optic nerve and nerve fiber layer of the retina to even low concentrations of solvents that solubilize or help stabilize other formulations such as emulsions. Though the moderate to high lipophilicity typical of this class may confer some resistance to vitreous degradation and prolong duration once injected the small molecular weight of on average about 500 daltons vs. for example Lucentis® at 40,000 daltons is inversely proportional to drug retention and hence duration. All of the molecules used in VEGF inhibition, including multi-receptor tyrosine kinase inhibition have chemotherapeutic application and have a risk of severe systemic side effects with high systemic absorption. This risk remains for intravitreal injection due to the high cell permeability of this class of drugs. Pazopantinib has undergone up to 10 Phase II efficacy trials between 2008 and 2014 for topical ant-VEGF treatment. However, none of the efficacy trials for Pazopantinib are for invitreal administration. The lack of intravitreal administration efficacy trials for pazopantinib is most likely due to its rapid intravitreal clearance estimated to be within hours for its molecular weight.
Thus, while there is a need in the art for a long-lasting effective inhibitor of angiogenesis and vascular leakage within the eye, particularly a safe and prolonged intravitreal, TKI's or MTKI's that have sufficient duration of activity and a reduced incidence of systemic side effects have to date not been discovered. Those MTKI's that have been tested have not met these ideals and have not been successful for this purpose.